1. FIELD OF THE INVENTION: The invention is directed to improvements in valves employed in subterranean wells, for example, safety valves, such improvements being directed to providing pressure equalization between the upper and lower faces of the valve head employed to engage the valve seat to facilitate opening same, and mechanism for selectively effecting the temporary locking of the valve in an open position or converting the temporarily locked open valve to a condition where it is permanently locked in its open position.
2. DESCRIPTION OF THE PRIOR ART: Valve mechanisms have been employed in subterranean wells for the primary purpose of effecting a reliable, positive closure of the bore of a production tubing string in the event of any emergency. The actual valving elements of heretofore known valves have comprised ball valves, flapper valves, poppet valves and axially shiftable block elements. Regardless of the type of valving element employed, there has been a problem of effecting the reliable opening of such a valve whenever a significant pressure differential existed between the lower surface of the valve element and the upper surface. There is, therefore, a need for a pressure equalizing mechanism which accomplishes the equalization of such pressure differential as an automatic consequence of an initial movement of the actuator employed to open the valve.
A common form of actuator for such a valve is an annular sleeve which is driven downwardly through the imposition of a controlled fluid pressure supplied from the top of the well head. There are often occasions in conducting testing of a well or replacement of down hole elements of the tubing string or other conduit where it is desirable to insure that the valve is mechanically locked in an open position and is not dependent upon maintaining its open position solely through the continued application of the control pressure.
Additionally, if it is necessary to remove the conduit carrying the valve from the well, it is very desirable that the valve be permanently locked in its open position during the removal operation so as to insure the ready drainage of any fluid trapped in the tubing string as the string is removed from the well.